A New Reaching Law Based Nonsingular Terminal Sliding Mode Control Scheme for the Servo System With Periodic Uncertainties

Abstract

A new control strategy is proposed to optimize the position-tracking accuracy of the servo system with disturbances and uncertainties, especially periodic uncertainties that commonly exist in industrial equipment working repetitively. First, according to the requirements of tracking accuracy, the position tracking error is categorized into various error bands, and a new reaching law based on the error bands is developed. The reaching law is composed of a linear term and a power term with variation coefficients. The designed reaching law can improve the convergence rate of minor errors and suppress the inherent chattering. Then, based on the new reaching law, a non-singular terminal sliding mode controller (NTSMC) with periodic adaptive compensation is developed. The control scheme is also composed of two parts: an NTSMC part and a periodic adaptive compensation part. Under periodic load torque variations and unmodeled system dynamics, fast convergence of position tracking errors is guaranteed by the NTSMC part, while tracking accuracy is enhanced by the periodic adaptive compensation part. The stability of the servo system under the control law is analyzed by Lyapunov theory. Simulations and experimental results show that high-precision tracking performance can be achieved under different load situations.INDEX TERMS error band based reaching law, periodic uncertainties, periodic adaptive control, nonsingular terminal sliding mode control.